1. Field of the Invention
The present invention relates in general to an optical disc drive, and more particularly, to an optical disc drive capable of adjusting the phase of a wobble clock with a frequency divider.
2. Description of the Prior Art
Over the past few years, storage media have rapidly increased in storage capacity due to demand for storing a tremendous amount of information. Of all the various kinds of storage media, optical discs have features of a low-cost, small-size, low-error-rate, long-storage-time, and high-density storage medium and are the most promising dominant storage medium in the future. Generally speaking, optical disc drives are used to read information stored on an optical disc. Examples of optical disc drives are known as compact disc drives (CD-ROM drives) and digital versatile disc drives (DVD-ROM drives) in the prior art. Some optical disc drives have the additional capability of being able to write data onto an optical disc, i.e., CD-R/RW, DVD+R/RW and DVD-R/RW drivers. Optical disc drives are used in music and video playback and are implemented in recording devices and other electronic devices.
In order to effectively manage the information stored on a digital versatile disc, the data storage region of the digital versatile disc is divided into many frames. Data can be stored in these frames according to a memory format. Therefore, while in a writing process for a rewritable digital versatile disc, the DVD drive has to identify the memory format of the rewritable digital versatile disc before the writing process. In order to record the related information concerning the memory frames, there are special addressing structures on the rewritable digital versatile disc to record the related information. According to the specifications of a recordable or a rewritable digital versatile disc, the related information recorded in the addressing structures is known as the address in pre-groove (ADIP).
It is well-known that the information of the ADIP is recorded in the wobble signal by a phase modulation technique, which means that the information is recorded according to the phase shift of a carrier. Every pair of record areas on an optical disc corresponds to 93 wobble cycles, and 8 wobble cycles of them are utilized to record an ADIP by phase modulation.
Please refer to FIGS. 1-3. FIGS. 1-3 are diagrams of schematic waveforms of the prior art wobble signals 4a, 4b, and 4c. The wobble signal 4a shown in FIG. 1 comprises 8 wobble cycles W0, W1, W2, W3, W4, W5, W6, and W7, which are utilized to record the information of an ADIP by phase modulation. As is shown in FIG. 1, a phase shift of 180° occurs at the beginning of the first phase-modulated cycle W0 of the wobble signal 4a. In addition, a phase shift of 180° also occurs between the wobble cycle W3 and the wobble cycle W4 of the wobble signal 4a. Consequently, the wobble signal 4a corresponds to an ADIP sync unit. Similarly, the wobble signal 4b shown in FIG. 2 comprises 8 wobble cycles W0, W1, W2, W3, W4, W5, W6, and W7, which are utilized to record the information of an ADIP by phase modulation. As is shown in FIG. 2, a phase shift of 180° occurs at the beginning of the first phase-modulated cycle W0 of the wobble signal 4b. In addition, a phase shift of 180° also occurs between the wobble cycle W0 and the wobble cycle W1 of the wobble signal 4b, and a phase shift of 180° further occurs between the wobble cycle W5 and the wobble cycle W6 of the wobble signal 4b. Consequently, the wobble signal 4b corresponds to an ADIP data unit having a corresponding logic level of 0. Likewise, the wobble signal 4c shown in FIG. 3 comprises 8 wobble cycles W0, W1, W2, W3, W4, W5, W6, and W7, which are utilized to record the information of an ADIP by phase modulation. As is shown in FIG. 3, a phase shift of 180° occurs at the beginning of the first phase-modulated cycle W0 of the wobble signal 4c. In addition, a phase shift of 180° also occurs between the wobble cycle W3 and the wobble cycle W4 of the wobble signal 4c, and a phase shift of 180° further occurs between the wobble cycle W5 and the wobble cycle W6 of the wobble signal 4c. Consequently, the wobble signal 4c corresponds to an ADIP data unit having a corresponding logic level of 1.
As is described above, the information of an ADIP unit is recorded in the wobble signal by phase modulation, therefore the optical disc drive is required to utilize an ADIP decoder to decode the information of an ADIP unit. Please refer to FIG. 4 in conjunction with FIG. 5. FIG. 4 shows a functional block diagram of a prior art optical disc drive system 10. FIG. 5 is a diagram of schematic waveforms of the wobble signals WBL, WBL′, and WBL″, and the wobble clock CLK, which are actually the operating clock waveforms related to the optical disc drive system 10 in FIG. 4 with time along the abscissa. The optical disc drive system 10 comprises an optical disc 12 and an optical disc drive 14. The optical disc drive 14 comprises an optical pickup 15, a first band-pass filter 16, a second band-pass filter 18, a wobble clock generator 20, a frequency divider 21, an ADIP decoder 22, and a controller 24.
As is well known in the specifications of a DVD+R disc drive or a DVD+RW disc drive, on the reflecting surface of the optical disc 12, there is a fine spiral track. The fine track is composed of two types of tracks, one being a data track to record data having a value of 0 or 1, and the other being a wobble track to record related addressing information. The data track has an interrupt and discontinuity record mark, and the wobble track has an oscillating shape. The surface of the wobble track protrudes beyond the reflecting surface of the optical disc 12. The data track is located inside a groove formed by the raised wobble track. The length of each record mark varies, and the reflection characteristic of the record mark is different from that of the other reflecting surface of the optical disc.
Consequently, the ADIP is recorded in the wobble track to assist the process of reading or writing data on the data track by the optical pickup 15. Thereby, the optical pickup 15 is able to extract the tracking information carried by the wobble track of the optical disc 12 and generates a wobble signal WBL. The wobble signal WBL is then forwarded to the first band-pass filter 16. The wobble signal WBL′ generated by the first band-pass filter 16 based on the wobble signal WBL is forwarded to both the second band-pass filter 18 and the ADIP decoder 22.
Traditionally, the first band-pass filter 16 is a band-pass filter having a low quality factor (Q-factor), and the second band-pass filter 18 is a band-pass filter having a high quality factor. Because of the first band-pass filter 16 having a low quality factor, the wobble signal WBL′ generated by the first band-pass filter 16 based on the wobble signal WBL has the component having a frequency outside the predetermined dominant band suffer from a slight decay as is shown in FIG. 5. On the contrary, because of the second band-pass filter 18 having a high quality factor, the wobble signal WBL″ generated by the second band-pass filter 18 based on the wobble signal WBL′ has the component having a frequency outside the predetermined dominant band suffer from a significant decay as is shown in FIG. 5.
The wobble signal WBL″ is then forwarded to the wobble clock generator 20. The wobble clock generator 20 is utilized to generate a reference clock CLK_REF based on the wobble signal WBL″. Traditionally, the frequency of the reference clock CLK_REF is higher than the frequency of the wobble signal WBL″. For instance, the frequency of the reference clock CLK_REF is 32 times as high as the frequency of the wobble signal WBL″. Accordingly, the frequency divider 21 is required to lower the frequency of the reference clock CLK_REF and generate the wobble clock CLK, for instance the frequency of the wobble clock CLK is 1/32 as high as the frequency of the reference clock CLK_REF. Thereafter, the ADIP decoder 22 is able to decode the ADIP of the wobble signal WBL based on the wobble clock CLK and the wobble signal WBL′. For instance, with the aid of the frequency divider 21, the non-phase-modulated wobble clock CLK is generated through the wobble clock generator 20 based on the phase-modulated wobble signal WBL″. Next, the ADIP decoder 22 performs an XOR logic operation over the wobble clock CLK and the wobble signal WBL′ to extract the ADIP of the phase-modulated wobble signal WBL. The ADIP generated is then forwarded to the controller 24. Thereafter, the controller 24 is able to perform a reading or writing process on the optical disc 12 based on the ADIP.
As aforementioned, the wobble signal WBL′ is generated by the first band-pass filter 16 having a low quality factor based on the wobble signal WBL. Subsequently, the wobble signal WBL″ is generated by the second band-pass filter 18 having a high quality factor based on the wobble signal WBL′. Afterward, the reference clock CLK_REF is generated by the wobble clock generator 20 based on the wobble signal WBL″. Then, the wobble clock CLK is generated by the frequency divider 21 based on the reference clock CLK_REF. Consequently, a phase delay occurs between the wobble signal WBL′ and the wobble signal WBL″, and the amount of the phase delay depends on the first band-pass filter 16 and the second band-pass filter 18. Therefore, as the ADIP decoder 22 generates the ADIP by decoding the wobble signal WBL′ with the aid of the wobble clock CLK, the phase delay may cause an error operation of the XOR decoding process.
Please refer to FIG. 6. FIG. 6 is a diagram of schematic waveforms of the wobble signal WBL′, the ideal wobble clock CLK, the real wobble clock CLK′, the ideal processing signal S1, and the real processing signal S2, which are the operating clock waveforms related to the ADIP decoder 22 in FIG. 4 with time along the abscissa. For the sake of clarity, the effects of the first band-pass filter 16 and the noise interference are not under consideration, and the ideal waveform of the wobble signal WBL′ is shown in the first waveform of FIG. 6. Then, if the phase delay caused by the second band-pass filter 18 is not under consideration, the ideal waveform of the wobble clock CLK is shown in the second waveform of FIG. 6. However, if the phase delay caused by the second band-pass filter 18 is under consideration, the real waveform of the wobble clock CLK′ is shown in the third waveform of FIG. 6. Obviously, there is a phase difference between the real wobble clock CLK′ and the ideal wobble clock CLK. In other words, the phase of the real wobble clock CLK′ lags the phase of the ideal wobble clock CLK. For instance, as is shown in FIG. 6, the phase difference the real wobble clock CLK′ and the ideal wobble clock CLK is 90°. After the ADIP decoder 22 performs an XOR operation over the wobble signal WBL′ and the wobble clock, two possible resultant waveforms are shown in FIG. 6. The fourth waveform of FIG. 6 shows the resultant waveform of the ideal processing signal S1 by an XOR operation over the wobble signal WBL′ and the ideal wobble clock CLK. The fifth waveform of FIG. 6 shows the resultant waveform of the real processing signal S2 by an XOR operation over the wobble signal WBL′ and the real wobble clock CLK′. Obviously, if the ADIP decoder 22 generates the ADIP by decoding the wobble signal WBL′ with the aid of the real wobble clock CLK′, the phase delay may cause an error operation of the XOR decoding process as is shown in FIG. 6.